Hi sweeties <3 Alexandra's been sick since Wednesday, poor girl, so I've spent most of the time taking care of her and comfort her. Therefore, again (!), this week's Friday Facts blogpost comes on a Sunday. Hope you understand...This time I feel the need of giving you ten facts about my favourite particle - the neutron:

neutrons are radioactive if they are "free" (alone, and not part of the nucleus of an atom)

neutrons have no charge - they are neutral, and can therefore "sneak" into another nucleus, and for example make it fission 😀

the recipe for a neutron is: 2 down quarks and 1 up quark (opposite to the proton that is made up of 2 ups and 1 down)

the half-life of a (free) neutron is about 10.2 minutes, and then it turns into a proton, and electron, and an anti neutrino. Meaning it beta decays 😀

the neutron was discovered by James Chadwick in 1932

neutrons have a mass, which is almost equal to the proton, but the neutron is a little bit heavier. Actually the mass of the neutron is 1.674927471×10−27 kg (or 0.00000000000000000000000000164927471 kg), and that's the same as 2.5 electron masses (electrons weigh really little) more than a proton

neutrons can make stuff radioactive - which is called neutron activation; so a normal, stable gold nucleus can for example be activated by a neutron and go from gold-197 (stable) into gold-198 (un stable) and then decay into mercury-198, which is stable

you can't make a nucleus entirely out of neutrons - you have to have at least one proton too, and then you have deuteron, or heavy hydrogen

number 8 is actually just sort of true; you can go to an extreme, and calculate how many neutrons you need to make a "nucleus" entirely out of neutrons (since neutrons have no charge, they don't repel each other, like protons do, but they don't stick together either - a little bit like two pieces of paper; if you put them together they will just fall apart), and since they do have a mass they will attract each other because of gravity between them. This means that if you have enough neutrons, you will make something that won't just fall apart; and that number is . Not exactly nuclear size...:P (Read more about that HERE)

when neutrons hit you, they will give you a dose that is dependant on their energy. The highest dose from a neutron comes when it has an energy of 1 million electron volts. If the neutron has lower or higher energy, the dose from it will be lower.

For some reason I imagine neutrons to be white 😛 How do you imagine the neutron to look?

Today I just wanted to tell you a little bit about neutrons, and why I think they're the coolest. You know, in a way they're like a Chanel purse - classical, and never out of style 😉

speaking of Chanel: I've been thinking that I should buy a black Chanel purse as a gift for my self when I have finished my PhD, but maybe I should consider the pink one instead...?

So here are my ten reasons why I think neutrons are really cool:

Neutrons have no charge

They decide if an atom is stable or radioactive

A single neutron can sneak its way into a nucleus and make fission <3

It's an unstable particle with a half life of a little bit more than 10 minutes

I sort of envision them as white dots, or tiny billiard balls...

A free neutron turns into hydrogen (meaning that the neutron is actually a radioactive particle - radioactivity is just soooo fascinating 😀 )

Neutrons are the "flame" in the fuel of a nuclear reactor

Neutrons gives different doses (of radiation) depending on their energy

You can make a neutron from a proton and a proton from a neutron (almost sounds like witchcraft, or something)

If neutrons have the right energy, they can do quite a lot of damage - but you can just use normal water as a shield, and you're fine 😉

I just love them - neutrons are without doubt my favorite. They're fabulous ✨

Do you have a favorite particle?

-------------------------------------------------

PS: I am working on Question of the month (which is actually not a nuclear physics one this first time) - the plan was to publish it yesterday, but since I (unfortunately? 😛 ) have another job than just being a blogger, I haven't been able to finish it yet , and I'm really sorry :/ However, I'm still inside my own "limits", since I said it would come this week, and even though it's Friday, it's not the end of the week just yet 😉

Today it´s 83 years since Chadwick´s paper in Nature: Possible Existence of a Neutron, where he predicted that there had to be a neutral particle (neutron <3<3<3) in the atomic nucleus, in addition to the proton.

"Up to the present, all the evidence is in favour of the neutron, while the quantum hypothesis can only be upheld if the conservation of energy and momentum be relinquished at some point."

He was right, of course, and in May the same year he had another paper in Nature - The Existence of a Neutron - and he got the nobel prize in physics in 1935 for the discovery of the neutron.

The multi-recycling of innovative uranium/thorium oxide fuels for use in the European Pressurized water Reactor (EPR) has been investigated. If increasing quantities of 238U, the fertile isotope in standard UO2 fuel, are replaced by 232Th, then a greater yield of new fissile material (233U) is produced during the cycle than would otherwise be the case. This leads to economies of natural uranium of around 45% if the uranium in the spent fuel is multi-recycled. In addition we show that waste radio-toxicities and decay heats are up to a factor of 20 lower after 103 years. Two innovative fuel types named S90 and S20, ThO2 mixed with 90% and 20% enriched UO2 respectively, are compared as an alternative to standard uranium oxide (UOX) and uranium/plutonium mixed oxide (MOX) fuels at the longest EPR fuel discharge burn-ups of 65 GWd/t. Fissile and waste inventories are examined, waste radio-toxicities and decay heats are extracted.

1 Introduction

Thorium is a fertile material that can easily be transformed into fissile 233U by thermal neutron capture. 233U does not exist in nature but is an excellent fissile material which has a higher η (∼2.3), the number of neutrons emitted per neutron absorbed, than the analogous fissile plutonium isotopes 239, 241Pu (∼1.7, ∼2.1) from the U/Pu cycle. This implies that the yield of new fissile material in fuels containing fertile 232Th will always be greater than for those containing fertile 238U, assuming a thermal neutron spectrum. Furthermore, the neutron capture/fission ratio of 233
sup>U (∼0.11) is lower than that of 239Pu (∼0.55) and five successive neutron captures on fertile 232Th are required to produce a trans-uranium element (TRU), while only one is necessary for fertile 238U. Therefore, production rates for the TRU’s, the major long-lived nuclear waste components will be much lower if 238U is replaced with 232Th.

We focus here on the EPR reactor and examine the consequences of removing significant quantities of fertile 238U from conventional UOX fuel and replacing it with fertile 232Th. This is achieved by blending thorium with uranium enriched to higher content of fissile 235U than the typical 4% needed for PWRs. We examine two new types of innovative fuel for the EPR, S20, a mixture of 20% enriched UO2 and ThO2, and S90, a mixture of 90% enriched UO2 and ThO2, and compare with conventional UOX fuel and MOX fuel fabricated from the plutonium recovered in spent UOX reprocessing.

The EPR is a Generation III + PWR concept, which is an evolutionary design rather than revolutionary and based on proven pressurized water technology - currently the most widely used worldwide.

In theory, light water reactors (LWRs) with a thermal neutron spectrum using 233U/232Th fuels can breed self-sustaining amounts of new fissile material since 2.3 neutrons are available per neutron absorbed, and indeed breeding was proven in the Shippingport Light Water Breeder Reactor [1]. However, for a light water power reactor with realistically long cycle lengths there will be significant losses of neutrons to captures on the hydrogen in the water coolant, the fission products, the control poisons, the 233Pa intermediate thorium cycle nucleus and the structural materials, and thus the breeding ratio will be less than unity and breeding will be impossible. For breeding ratios of less than one, the thorium cycle will not be self-sustaining and the reactor will be dependent on a supply of some fissile material from the uranium cycle – either new fissile 235U or 239,241Pu.

Concepts
dedicated exclusively as thorium cycle breeder reactors have been suggested, e.g. the Thorium Molten Salt Reactor [2] and the use of thorium in sodium critical reactors [3], or in subcritical accelerator driven systems [4-6]. However, these technologies are very different from current power reactor designs and cannot use existing cycle infrastructure. A large amount of research and development is needed for these systems and thus commercial power production could be decades into the future. Since LWRs comprise around 80% of the world fleet of operating plants, the fastest way to explore the potential of thorium is through the use of innovative solid fuels in the existing infrastructure of operating plants.

The once through cycle (OTC) is the cheapest fuel cycle in the short term. However, the potential energy content of the residual fissile and fertile isotopes is lost, and the OTC also gives the largest possible volume of high-level waste. The potential energy content of the spent fuel provides an incentive to recover the fissile isotopes. Fuel recycling also reduces the mass of high-level waste and the time of high radio-toxicity of waste, thus reducing the requirements for both the number of repositories and the duration of geological storage. The goal of the present work is to examine thoriated fuels as an alternative to present MOX recycled fuels that should provide greater economy of uranium resources and lower waste inventories.

2EPR simulations with the MURE code

An EPR assembly based on a 17 × 17 lattice was modeled using MURE (MCNP Utilities for Reactor Evolution), based on the Monte-Carlo neutron transport code MCNP5 [7]. MURE is a precision research code that has been developed jointly at the Institut de Physique Nucléaire d’Orsay (IPNO) and the Laboratoire de Physique Subatomique et Cosmologie (LPSC) of Grenoble [8]. MURE performs calculations of the time-evolution of reactor fuels with full 3D geometry. Consecutive MCNP calculations are performed to determine reaction rates and deduce core material evolution over time at a constant reactor power by solving the set of coupled differential equations for the production and destruction of isotopes.